Assessment of potentially toxic trace elements contamination in groundwater resources of the coal mining area of the Korba Coalfield, Central India

Exploiting coal by open-cast mining often poses a threat to groundwater chemistry due to leachate of contaminants from the mine drainage water. In order to assess this, groundwater, river water and mine water samples were collected from Korba Coalfield and analysed for potentially toxic trace elements (PTEs) along with in situ parameters. Thereby, an integrated approach of pollution evaluation indices [heavy metal pollution index (HPI), heavy metal evaluation index (HEI) and contamination index (Cd)] and statistical techniques are applied to the results. Paired-sample t tests reveal that the PTE concentrations of the pre-monsoon samples are higher than those of the post-monsoon samples. At a few locations, the concentration of Fe (56%), As (56%), Al (26%), Mn (19%) in pre-monsoon and Mn (46%), Ni (15%), Ba (15%), Pb (8%) in post-monsoon seasons exceeds the acceptable limit of Indian drinking standards. However, HPI values are below the critical pollution index value of 100 in both seasons in spite of an excess of these elements. The pollution indices evaluated by the multiple of the mean values approach reveal that 100, 94, 87% of the pre-monsoon and 92, 92, 85% of the post-monsoon samples belong to the “low-to-medium” category with respect to the HPI, HEI and Cd indices. The thematic map depicting the spatial distribution of the contamination index (Cd) testifies the role of a “dilution effect” that results in lower pollution loads in the post-monsoon samples than the pre-monsoon ones. The results of cluster analysis confirm that the quality of the water is mainly controlled by geogenic processes and anthropogenic inputs, besides dilution effects.